Most bears aren’t aggressive unless you’re anywhere near their cubs. If you’re ever walking in the wild and you see bear cubs you want to turn and get the hell out of there. Their mothers will not stop to ask questions before tearing you apart.
Bears are common in the wilds of the USA and Canada, as well as the Arctic regions, parts of Eastern Europe and East Asia. Bears have no interest in eating humans as they prefer to carry on lifting picnic baskets. They can be aggressive though if they perceive you as a threat or competition.
Grizzly bears in particular can be extremely aggressive and on average 2 people are killed every year in North America. If one comes from you there really isn’t much you can do about it except that hope that when it charges you it’s bluffing. Check out the photos of this grizzly going for a group of people fishing.
The most important thing is to avoid meeting bears in the first place. If camping in bear country, make sure your food is hung off the ground by a rope from a tree a reasonable distance from where you pitch your tent. If you happen to meet a bear just back off slowly without causing alarm. Failing that causing a good deal of noise may scare it away.
It’s thought that dogs and bears have common ancestors. Perhaps that’s why these enormous predators seem cute even when they’re fighting.